I'm needing to rebuild my garage roof. The garage was built in the 30’s/40’s and was stick framed with a 1x8 ridge board, 2x4 rafters, 1x8 collar ties and 1x8’s running across the bottom of the rafters (would that be considered a tie beam or a joist?). I’d like to reframe the roof using the stick method (no trusses) but I’d like to bring the lumber dimensions up to current code sizes. If possible I’d like to skip having the tie beams at the bottom to give me more head room. The garage is 18’4” from wall to wall (square) and has a modified gable style roof (pictures are here) http://picasaweb.google.com/callumh/GettoGarage/photo#4942884769487257618.

Thanks

 

1st, there are a couple of standard methods employed to keep a garage "square", since they seldom have finished ceilings or intermediate walls that an occupied structure does.

One is "X'ed", lapped 1x's installed too diagonal corners.
Another is a diagonaly placed 2x at each corner, let into the
top plates, 6' from each opposinge corner.

Probably some thing you could address with shear panel.

A full hip roof will meet your needs for the ceiling height, tying the hips diagonally with double 2x6's at mid run.